1. Field of the Invention
The invention generally relates to a method for nondestructively measuring principal components of complex stress fields in a test article, and more particularly to an improved method for measuring stress ultrasonically.
2. Description of the Prior Art
The use of nondestructive methods based upon ultrasonic birefringence has been suggested for measuring stress level changes in laboratory specimens of anisotropic materials. However, only one component of three dimensional stress fields normally are obtainable through use of such methods. While the birefringence methods tend to work reasonably well in uniform laboratory specimens, where only one principal stress axis exists, it is noted that stress is a complex force field and where two or more of the stress components are near the same magnitude, birefringent differentials may be near zero, particulary when large stress levels actually exist in a specimen.
Therefore, there currently exists a need for a practical nondestructive method for measuring orthogonal components of complex stress fields in test articles subjected to loading in non-laboratory environments.
It is, therefore, a general purpose of the instant invention to provide a nondestructive method of measuring sub-surface biaxial stress fields in engineering structures which is simple and economic to employ and overcomes the aforementioned disadvantages.